Just my 2 credits, from my own experience in running games at conventions:
* Keep it (very) simple. Four hours is not a long time. These players don't know you and don't know how you run games. You want themes and goals to be very obvious, because anything less obvious will be a complete mystery to your players.
* I avoid chargen at the table. In my experience, it's a timesink and it tends to dampen the mood. I would suggest you creating about three or four times as many pre-gen characters as you expect to have players (so if you plan to run 4 people through the game, have 16 characters available). Have each character have a name and preferably art for the character (eg; a character portrait). Write a character brief - a short paragraph, ideally a single sentence that sums the character up (it's possible, they do it for character briefs when pitching TV shows or games all the time); this gives the player broad strokes to get a handle on the character, let the character fill in any blanks with RP. Pregens allow you to save time, get the ball rolling ASAP, and allow you to craft characters who will be relevant in your game (make sure all the pregens are relevant). (Also, I personally feel including 'death in chargen' as a quirk of Traveller is going to have the opposite effect of selling the game to your players.)
* Absolutely have a reason why the players should be working together. Four hours isn't long enough (IMO) to have some clever guy trying to play traitor or anything subtle like that. The players could all be prisoners of pirates looking to get away, a team of archeologists, a military unit, anything so they don't waste time sizing each other up and negotiating and so on (and so you don't have to risk that contrarian clown pulling the metagame where they intentionally try and have a player get kicked from the group just to see what the player does or to see how you as the GM handle the situation).
* I like the idea of the players being pursued. Players tend to dwadle a lot in RPGs if left to their own devices. While this might be okay for some groups, I think it's bad for a con game which will be one session and likely of medium length. So it's ideal to have some thematic element that reinforces to players they're on the clock and they have to keep moving.
* I'm iffy on the idea of the 'ruins of a long-dead empire' for a con game. I feel that a GM shouldn't use an unusual or exotic location unless that location is going to be used for something that cannot be found in a more mundane setting. What would a long-dead ruins offer that some more mundane setting wouldn't? For me "ruins of a long-dead empire" suggests mystery and exploration, two themes that don't work so well when the players are being pursued.
Also, alien ruins can be hard to describe in a way that makes a vivid image pop in your player's minds. Compare:
"You see tall towers of irregularly shaped pinkish stone that tower hundreds of meters into the air, their purpose unknown. There's at least a dozen in a cluster, they curve oddly from their foundations, the effect like fan coral on earth. As you reach the top of the low rise you're hiking up, you notice scattered at the base of these are hundreds of pear-shaped buildings, each about four storeys tall, connected by a webwork of catwalks that look from a distance like cobwebs compared to the size of the buildings. The entire area gives the impression of forlorn abandonment, the round windows in the pear-shaped buildings remind you of skulls - perhaps not human skulls but skulls nevertheless. Unlike the towers, the pear-shaped buildings look like they were made from some sort of brick-red material, like terra-cotta flowerpots, though some seem to shimmer and sparkle faintly in the weak daylight, though you're not sure if that's some ancient power system still working or just some sort of reflection of the light from the material the buildings are made from. The pinkish towers feel somehow lonely and desperate, rising from the reddish sand of the world, like skeletal fingers of a doomed spacefarer reaching up from his dusty grave towards the purplish sky and the twin ghostly spheres of the moons above, beyond, to the freedom of outer space."
vs.
You come upon an abandoned megacorporate mining settlement. These are very common in the hypercapitalist Third Imperium, set up to mine some material or another, then abandoned just as fast when the lode played out. They've been left abandoned since it's cheaper just to set up a new one at the new site than to pick up the current one. There's these multi-purpose tubular prefabs all rigged up so it looks like those hamster tubes except made of rusting metal, broken up by these repurposed shipping containers piled atop each other and used as housing or maybe storage - it's hard to tell and it's all rusting away. There's also the occasional geodesic green house domes, covered with the same fine reddish dust of the moon, though most of the domes are dark and some have their transparent roofs collapsed."
While both will evoke images, I think the latter is a lot more accessible than the former. The former I think will make the players want to explore and investigate, the latter will have the players more likely to look for shelter, transportation, weapons, and possibly an ambush against their pursuers.
